Over the years, many composites have been developed for reducing loud noise such as noise from heavy machinery, and engine noise from trucks and aircraft.
As an example of an acoustical composite currently used to reduce aircraft noise, there exists a composite comprising two pounds per cubic foot density fibrous glass wool sealed in polybag on both sides of a lead/vinyl sheeting.
In addition to the above-described foam-barrier-foam-facing acoustical composites for aircraft, acoustical composites of the foam-barrier type are known which provide noise transmission loss but do not provide noise absorption as well.
For example, U.S. Pat. No. 4,056,161, discloses a foam-barrier-wear layer composition which provides noise transmission loss. The outer wear layer can be polyvinyl chloride reinforced with fabric. The foam layer can be a low density polyester based polyurethane foam having open cells or pores. The intermediate high density barrier layer comprises a vinyl plastisol composition with a particulate material such as barium sulfate particles dispersed therein. The sound barrier layer also acts as a bonding layer for adhering both the outer layer and the foam layer. This product is used for tractor cab mats, fire wall barriers, headliners, etc. on heavy equipment vehicles, as well as for pipe wrap.
U.S. Pat. No. 4,110,510 discloses a sound barrier material comprised of a polyvinyl chloride impregnated fiber sheet or mat having a rubbery coating of a barium sulfate containing chlorinated polyethylene on each side. The fiber sheet or mat is preferably fiber glass. A foam, preferably polyurethane, having a density of 1.5 to 2.5 pounds per cubic foot is further laminated to one of the coating layers and functions as a decoupler to the mass barrier. This type of product is typically applied to noise enclosures and as pipe wrap for in-plant retrofit.
U.S. Pat. No. 4,340,129 discloses a flexible acoustical laminate construction comprising a weighted polymeric lamina having a surface density of at least about 0.5 lb/ft.sup.2, and, adhered thereto, a polymeric foam composition designed to have a loss factor v of at least about 0.4 at 25.degree. C. This acoustical laminate, like the two aforementioned, is a foam-barrier construction (decoupled mass) except that a highly plasticized polyvinylchloride foam is the decoupler rather than open cell polyurethane foam. This material is used, primarily, for cabliners in heavy equipment.
Despite the known compositions for reducing noise levels, there still remains room for improvement, and, in particular, there still remains room for improvement in acoustical composites which not only reduce noise transmission loss, as the above-mentioned foam-barrier type constructions, but which also absorb noise as well. Further, there remains room for improvement in acoustical composites which provide both noise transmission loss and noise absorption in aircraft and also are suitably light weight and flame and smoke retardant.